Fork lift with laterally travelling system

ABSTRACT

A fork lift with a laterally travelling system, wherein when a running mode is switched from a normal running in which right and left front wheels and rear wheels face in a longitudinal direction to a lateral running, rotating means is operated to rotate a turning member about a vertical axis in order to change the direction of the front wheels relative to that of a vehicle body, a change in running direction can be performed smoothly because the front wheels are formed integrally with a running drive device, and the front wheels are driven in forward and reverse directions by the running drive device after the front wheels are turned to face sideways so that a fork lift can run laterally and the rear wheels can be changed in direction in a follow-up manner by a turning caster system or can be changed in direction forcibly in the same manner as the front wheels, whereby the wheels of a drive system, though the fork lift is of a type capable of performing a normal forking operation, can be steered to face sideways so that it can run laterally to, for example, perform transportation of long materials with ease through a fork.

TECHNICAL FIELD

The present invention relates to a fork lift with a laterally travellingsystem which can switch the fork lift to lateral running.

BACKGROUND ART

Conventionally, vehicles having a laterally travelling system have beenseen among large-scale transporters, some kinds of loaders and the like,and reach-type electric vehicle type fork lift devices. Furthermore,there are also side fork lifts for handling long materials, which have amast or forks installed in a lateral direction with respect to themovement of the vehicle. However, there is no counter-type fork liftwhich has a function similar to that of a side fork capable of lateralmoving in addition to ordinary operational functions. In order toachieve a fork lift of such kind, it is necessary to steer front wheelswhich are drive wheels in a perfectly lateral direction.

More specifically, in a conventional fork lift 1 as illustrated in FIG.23, a pair of right and left-hand front wheels (drive wheels) 3 areprovided to a front portion of a vehicle 2, a pair of right andleft-hand rear wheels (steering wheels) 4 are provided to a rear portionthereof, and a driver's room 5 is provided above the front portion ofthe vehicle 2. A vertically extendable mast 6 is provided in the frontend section of the vehicle 2 to be rotatable in the front-and-reardirection by means of a coupling axle 7 extending in the lateraldirection of the vehicle, and a tilt cylinder 8 for performingfront-and-rear rotation is provided between the vehicle 2 and the mast6.

The mast 6 comprises a pair of right and left-hand outer frames 9 on thefork lift 1, and a pair of right and left-hand inner frames 10 guided onthe outer frames 9 to be able to move vertically, a lift cylinder 11provided between the outer frames 9 and inner frames 10. Furthermore, alift bracket 12 guided by the inner frames 10 to be able to movevertically is provided, and a pair of right and left-hand forks 13 areprovided to this lift bracket 12 via a pair of upper and lower fingerbars.

A seat 15, and a handle 16 or the like disposed to the front of thisseat 15 are provided in the driver's room 5, and above these elements, ahead guard 19 is provided via front pipes 17 and rear pipes 18projecting from the vehicle body 2. A counter weight 20 is provided onthe vehicle body 2, to the rear of the seat 15.

However, in the conventional fork lift 1 described above, since theright and left-hand front wheels 3 are driven by a common travel drive,it is not possible to steer these front wheels 3 in a perfectly lateraldirection, and hence lateral running cannot be achieved.

DISCLOSURE OF THE INVENTION

Therefore, it is a first object of the present invention to provide afork lift with a laterally travelling system so that the front wheelsforming the drive wheels can be steered to face directly sideways,whilst being capable of performing ordinary fork operations.

It is a second object of the present invention to provide a fork liftwith a laterally travelling system which allows adjustment of linearmovement and change of the direction of the vehicle body during lateralrunning.

It is a third object of the present invention to provide a fork liftwith a laterally travelling system which permits the vehicle to readilyturn during lateral running.

It is a fourth object of the present invention to provide a fork liftwith a laterally travelling system which allows the front wheels tosteer, with the mast being disposed between the right and left-handfront wheels.

In order to achieve the first object described above, the fork lift witha laterally travelling system according to the present invention ischaracterized in that a pair of right and left-hand front wheels and apair of right and left-hand rear wheels are provided in a steerablefashion on a vehicle body, the pair of right and left-hand front wheelsare coupled respectively to driving shafts of travel drive devices, bothtravel drive devices are installed on turning members provided rotatablyabout a vertical axis with respect to the vehicle body, rotating meansfor performing rotation of the turning members is provided, a mast isprovided on the front end of the vehicle body, and forks are provided onthe mast.

According to the present invention described above, during normalrunning, the right and left-hand front and rear wheels face in thefront-and-rear direction. Thereupon, by operating a lift lever, theforks are raised or lowered along the mast, and prescribed forkoperations can be performed. When switching from normal running tolateral running, rotating means is actuated first and the turningmembers are rotated about the vertical axis, whereby the front wheelscan be steered (to be in a perfectly lateral direction) with respect tothe vehicle body. Here, since the front wheels are respectively formedintegrally with running drive devices, it is possible to perform thisturning operation readily and smoothly. After steering the front wheelsin a perfectly lateral direction in this manner, the fork lift can becaused to run laterally in the right and left direction, by driving thefront wheels in the forward and reverse directions by means of thetravel drive devices. In so doing, follow-up steering of the rear wheelsis effected by means of a turning caster system, or alternatively, therear wheels are steered forcibly in a similar manner to the frontwheels.

In this way, in the present invention, it is possible to perform lateralrunning by steering the driving front wheels so as to face in aperfectly lateral direction, while using normal fork operations. Henceit is possible to readily convey long materials, for example, by meansof the forks.

In order to achieve the second object described above, in the firstaspect of the fork lift with a laterally travelling system according tothe present invention, the rotating means is constituted such that thetwo turning members are operated to turn in mutually opposing directionsby means of a common actuation device.

According to this first aspect of the invention, when switching fromnormal running to lateral running, it is possible to steer the frontwheels (to a perfectly lateral direction) with respect to the vehiclebody by actuating the common actuation device of the rotating means soas to rotate the turning members in mutually opposing direction aboutthe vertical axes. In this manner, after steering the front wheels to aperfectly lateral direction, the fork lift can be made to run laterallyin the right and left direction, by controlling and rotating the frontwheels in mutually opposing directions by means of the travel drivedevices.

Moreover, when performing lateral running, in other words, in lateralrunning mode wherein the two front wheels are steered laterally withrespect to the vehicle body, it is possible to readily correct deviationcaused in the linear movement of the vehicle by road surface conditionsor the weight balance of the vehicle, by slight actuation of theactuation device to steer the two front wheels inwards or outwards by asmall angle. Moreover, by steering the front wheels inwards or outwards,the direction of the fork lift can also be changed to some extent duringlateral running, and hence steering during lateral running can beperformed.

Moreover, in a second aspect a fork lift with a laterally travellingsystem according to the present invention, the rotating means comprisescoupling sections of the turning members disposed in mutually opposingdirections in the front-and-rear direction with respect to the verticalaxis; a link member in the lateral direction of the vehicle, the linkmember being coupled between these coupling sections to enable theturning members to be relatively rotatable; and an actuation device formoving this link member in the lateral direction of the vehicle.

According to this second aspect of the invention, it is possible tosteer the front wheels readily and reliably with respect to the vehiclebody by moving the link member in the lateral direction of the vehicle,by means of the actuation device.

In order to achieve the third object described above, in the thirdaspect of the fork lift with a laterally travelling system according tothe present invention, when the rotating means is operated to rotate theturning members, the two drive wheels laterally directed are displacedin the front-and-rear direction.

According to this third aspect of the invention, by controlling androtating the drive wheels by means of the travel drive devices, afterthe drive wheels have been steered to be in perfectly lateraldirections, in other words, by controlling and rotating the right andleft-hand drive wheels in such a manner that the rotational directionsand the speeds of revolutions thereof are the same, the fork lift can bemade to travel laterally in a right and left direction. Moreover, sincethe two drive wheels steered directed to be perfectly lateral aredisplaced in the front-and-rear direction of the vehicle, whenperforming lateral running, a turning force to the right or left can acton the vehicle, by simply differentiating the speeds of revolutions ofthe right and left-hand drive wheels by operating a handle or the like.Hence, lateral running can be performed while steering the vehiclereadily in the longitudinal direction (front-and-rear direction)thereof, and any deviation caused in linear movement of the vehicle bythe road surface conditions or the weight balance can be readilycorrected.

In order to achieve the fourth object described above, in a fourthaspect of a fork lift with a laterally travelling system according tothe present invention, the mast is installed between the right andleft-hand front wheels at the front end of the vehicle to be rotatablein the front-and-rear direction by means of a coupling axle disposed inthe lateral direction of the vehicle above the front wheels, arotational drive device for effecting front-and-rear rotation isprovided between the vehicle body and the mast, and when the mast isrotated by this rotational drive device, the lower section of the mastis moved to a position where the mast does not interfere with thesteering of the front wheels.

According to this fourth aspect of the present invention, during normalrunning, the mast assumes an upright attitude, the lower section thereofbeing disposed between the right and left-hand front wheels, and hencethe fork lift can be formed without creating a long front overhang. Theoperation of switching from normal running to lateral running can beperformed by rotating (inclining) the mast about the coupling axle byoperating the rotating drive device and moving the lower section thereofto a position where the mast does not interfere with the steering of thefront wheels, steering the front wheels to a 90° position (to bedirected laterally) with respect to the vehicle body, and rotating themast about the coupling axle by reverse operation of the rotating drivedevice to return the mast to the upright attitude. Thereby, the forklift can be made to travel laterally, while performing smooth turningwithout any hindrance and without creating a long front overhang.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a fork lift with a laterally travelling systemduring normal running, illustrating a first embodiment of the presentinvention;

FIG. 2 is a partially cutaway front view of a front wheel section of thefork lift with a laterally travelling system;

FIG. 3 is a schematic plan view of the fork lift with a laterallytravelling system during normal running;

FIG. 4 is a schematic plan view of the fork lift with a laterallytravelling system during lateral running;

FIG. 5 is a side view of a fork lift with a laterally travelling systemduring normal running, illustrating a second embodiment of the presentinvention;

FIG. 6 is a partially cutaway front view of a front wheel section of thefork lift with a laterally travelling system;

FIG. 7 is a schematic plan view of the fork lift with a laterallytravelling system during normal running;

FIG. 8 is a schematic plan view of the fork lift with a laterallytravelling system during lateral running;

FIG. 9 is a side view of a fork lift with a laterally travelling systemduring normal running, illustrating a third embodiment of the presentinvention;

FIG. 10 is a partially cutaway front view of a front wheel section ofthe fork lift with a laterally travelling system;

FIG. 11 is a plan view of a lateral running operating section of thefork lift with a laterally travelling system;

FIG. 12 is a schematic plan view of the fork lift with a laterallytravelling system during normal running;

FIG. 13 is a schematic plan view of the fork lift with a laterallytravelling system during lateral running;

FIG. 14 is a schematic plan view of the fork lift with a laterallytravelling system during lateral running adjustment;

FIG. 15 is a side view of a fork lift with a laterally travelling systemduring normal running, illustrating a fourth embodiment of the presentinvention;

FIG. 16 is a partially cutaway front view of a front wheel section ofthe fork lift with a laterally travelling system;

FIG. 17 is a plan view of a front wheel section of the fork lift, (a)during linear running and (b) during lateral running;

FIG. 18 is a schematic plan view of the fork lift with a laterallytravelling system, (a) during linear running and (b) during lateralrunning;

FIG. 19 is a schematic plan view of the fork lift with a laterallytravelling system, (a) during steering of the rear section and (b)during steering of the front section;

FIG. 20 is a schematic plan view of the fork lift with a laterallytravelling system, (a) during linear running and (b) during lateralrunning;

FIG. 21. is a side view of a fork lift with a laterally travellingsystem during normal running, illustrating a fifth embodiment of thepresent invention;

FIG. 22 is a side view of the fork lift with a laterally travellingsystem during lateral running; and

FIG. 23 is a side view of a fork lift, illustrating an example of aprior art.

BEST MODE FOR CARRYING OUT THE INVENTION

A first embodiment of the present invention is described below withreference to FIG. 1 to FIG. 4.

In the first embodiment, constituent elements which are the same orsubstantially the same as those in the prior art example (FIG. 23)described above are similarly labelled, and further explanation thereofis omitted here. Specifically, 1 is a fork lift, 2 is a vehicle body, 3are front wheels (drive wheels), 4 are rear wheels (steering wheels), 5is a driver's room, 6 is a mast, 7 is a coupling axle, 8 is a tiltcylinder, 9 is an outer frame, 10 is an inner frame, 11 is a liftcylinder, 12 is a lift bracket, 13 is a fork, 15 is a seat, 16 is ahandle, 17 is a front pipe, 18 is a rear pipe, 19 is a head guard, and20 is a counterweight.

The pair of right and left-hand front wheels 3 and the pair of right andleft-hand rear wheels 4 are provided such that they are respectivelysteerable to be angled 90° (steerable in a perfectly lateral direction)with respect to the vehicle body 2. More specifically, the pair of rightand left-hand front wheels 3 are coupled to hydraulic motors 21 by meansof rims 3A thereof being respectively attached directly to a rotatingflange (one example of a driving shaft) 22 of the hydraulic motor (oneexample of a travel drive) 21, via a coupling tool 23.

A mount of each hydraulic motor 21 is attached in a lateral direction toa vertical plate section of an inverse L-shaped turning member 24. Alateral plate section of the turning member 24 is provided to thevehicle body 2 to be rotatable about a vertical axis 27 via a bearing 25and a vertical axle 26. In this case, the vertical axis 27 is positioneddirectly above the front wheel 3. The right and left-hand turningmembers 24 are coupled by means of a link 28 or the like, and arerotated by means of a common turning cylinder (an example of rotatingmeans) 29, whereby the right and left-hand front wheels 3 are caused tosteer in mutually opposing directions in such a manner that they face ina perfectly lateral direction.

An engine 30 and a pair of hydraulic pumps 31 driven by the engine 30are provided on the vehicle body 2. The corresponding hydraulic pumps 31and the hydraulic motors 21 are coupled by means of tubes (hydraulichoses or the like) 32 in such a manner that the hydraulic pumps 31correspond respectively to one of the hydraulic motors 21, in otherwords, in such a manner that a two-pump two-motor type hydraulic drivesystem (HST system) is formed.

Rims 4A of The pair of right and left-hand rear wheels 4 are installedin such a manner that respective rims 4A thereof are rotatable withrespect to the vertical plate section of a turning member 34. Thelateral plate section of each turning member 34 is provided to thevehicle body 2 to be rotatable about a vertical axis 37 by means of abearing 35 and a vertical axle 36. In this case, the vertical axis 37 ispositioned directly above the rear wheel 4. In other words, the pair ofright and left-hand rear wheels 4 are steered in a follow-up steeringmanner by use of a turning caster system.

Explained below is the operation in the first embodiment describedabove.

The solid lines in FIG. 1 and FIG. 2, and FIG. 3 illustrate a state ofnormal running, where the right and left-hand front wheels 3 and theright and left-hand rear wheels 4 are facing in the front-and-reardirection. A fork lift 1 of this kind can be driven to travel by anoperator seated on the seat 15 in the driver's room 5 and operating thehandle 16.

By operating a lift lever to actuate the lift cylinder 11, the fork 13can be raised or lowered along the mast 6 via the lift brackets 12 andthe like, and hence required fork operations can be performed. Further,by operating the tilt lever to actuate the tilt cylinder 8, the mast 6can be rotated (inclined) about the coupling axle 7, and therefore theattitude of the forks 13 can be changed via the lift brackets 12 or thelike.

When changing from such a normal running mode to a lateral running mode,a lever-type lateral mode switch (not shown) is operated first, then theturning cylinders 29 are actuated by inclining the lever, and theturning members 24 are rotated about the vertical axis 27 via the link28. Thereby, as illustrated by the virtual lines in FIG. 1 and FIG. 2and in FIG. 4, the front wheels 3 are steered 90° (steered to be in aperfectly lateral direction) with respect to the vehicle body 2.

Here, since the front wheels 3 are respectively formed integrally withthe hydraulic motors 21, this steering to a 90° position is performedsmoothly. Further, since each vertical axes 27 are positioned directlyabove the front wheels 3, the front wheels 3 or the like can be steeredto a 90° position in a compact manner.

Steering of the front wheels 3 in this manner, in other words, thesteering of the front wheels 3 to be in a perfectly lateral direction isdetected by a sensor which makes an indicator lamp to light up, wherebythe lateral running mode can be assumed. Consequently, by supplyinghydraulic pressure from the pair of hydraulic pumps 31 driven by theengine 30 to the corresponding hydraulic motors 21 via the pipes 32,according to the forward or reverse control performed in the driver'sroom 5, the front wheels 3 are driven in the forward or reversedirection, and hence the fork lift 1 can travel laterally in the left orright direction. In so doing, the pair of rear wheels 4 forming aturning caster system perform follow-up steering.

By performing lateral running in this way, it is possible, for example,to readily convey elongate objects by means of the forks 13. Correctionof linearity in the lateral running can be readily performed by minuteoperation of the turning cylinders 29 by inclining the lever in thefront-and-rear direction so as to perform minute adjustment of the angleof the front wheels 3.

Moreover, by adopting a two-pump two-motor type hydraulic drive systemfor the drive of the fork lift 1, the steering during normal running asdescribed above can be performed by controlling the direction ofrotations of the front wheels 3 and the difference in number ofrotations thereof by means of a handle wheel, but in the lateral runningmode, this steering system is stopped electrically.

Next, a second embodiment of the present invention is described withreference to FIG. 5 to FIG. 8.

In this second embodiment, constituent elements which are the same orsubstantially the same as those in the first embodiment described above(FIG. 1-FIG. 4) are similarly labelled, and detailed explanation thereofis omitted here.

The pair of right and left-hand front wheels 3 are coupled to electricmotors 41 by means of the rims 3A thereof respectively attached directlyto a rotating flange (driving shaft) 42 of the electric motor (anotherexample of a travel drive) 41 by means of a coupling tool 23. A battery43 is mounted in the vehicle body 2, and a controller 44 is attached tothis battery 43. A cable 45 from the controller 44 is connectedrespectively to each electric motor 41.

Explained below is the operation in the second embodiment describedabove.

The solid lines in FIG. 5 and FIG. 6 and the diagram in FIG. 7illustrate a normal running mode, where the right and left-hand frontwheels 3 and the right and left-hand rear wheels 4 are facing in thefront-and-rear direction. Therefore, by supplying electric power of thebattery 43, which has been controlled by the controller 44, to therespective electric motors 41 via the cables 45, the front wheels 3 aredriven in forward and reverse directions, whereby the fork lift 1 cantravel forwards or rearwards.

When switching from this normal running mode to a lateral running mode,as illustrated by the virtual lines in FIG. 5 and FIG. 6 and in thediagram in FIG. 8, the front wheels 3 are steered to a 90° position withrespect to the vehicle body 2 (steered to be in a perfectly lateraldirection). Since the front wheels 3 are integrally formed with theelectric motors 41, respectively, this steering to a 90° position isperformed readily and smoothly.

Steering of the front wheels 3 in this manner is detected by a sensorwhich makes an indicator lamp to light up, whereby the lateral runningmode is entered. Therefore, by supplying the electric power of thebattery 43, which has been controlled by the controller 44, to therespective electric motors 41 via the cables 45, the front wheels 3 aredriven forwards or rearwards, whereby the fork lift 1 can travellaterally in the left or right direction.

Next, a third embodiment of the present invention will be described withreference to FIG. 9 to FIG. 14.

In the third embodiment, constituent elements which are the same orsubstantially the same as those in the first embodiment described above(FIG. 1 to FIG. 4) are similarly labelled, and further explanationthereof is omitted here.

Rotating means 50 for causing rotation of the turning members 24 isprovided, and this rotating means 50 is constituted in such a mannerthat the turning members 24 are caused to turn in mutually opposingdirections by a common actuation device. In other words, vertical pins(one example of a coupling section provided on the turning member) 51are provided respectively on the lateral plate sections of both rotatingmembers 24 in such a manner that the two vertical pins 51 are positionedin opposite directions with respect to the vertical axis 27,respectively, to the front and to the rear of the vertical axis 27.

A link member 52 is provided in the lateral direction of the vehicle,and either end of this link member 52 is coupled in a relativelyrotatable fashion to one of the aforementioned vertical pins 51. Aturning cylinder (one example of an actuation device) 53 for causing thelink member 52 to move in the lateral direction of the vehicle, isprovided between the vehicle body 2 and the link member 52 at thecentral portion in the longitudinal direction thereof. One example ofrotating means 50 is constituted with the elements 51-53 and the like.

The rear wheel 54 is constituted by a parallel pair of right andleft-hand wheels, the respective rims 54A of which are attachedrotatably to vertical plate sections of a common turning member 55, andthe lateral plate section of this turning member 55 is providedrotatably about a vertical axis 58, with respect to the vehicle body 2,by means of a bearing 56 and vertical axle 57. In this, the verticalaxis 58 is positioned in the central portion between the two rear wheels54. This means that the rear wheels 54 are steered in a follow-upsteering manner by means of the caster system.

The operation in the third embodiment of the present invention describedabove will be explained below.

The solid lines in FIG. 9 and FIG. 10, and the diagrams in FIG. 11(a)and FIG. 12 illustrate a normal running mode. By retracting the turningcylinder 53 and causing the link member 52 to move in the direction ofretraction, the right and left-hand front wheels 3 and the rear wheels54 are oriented in the front-and-rear direction.

When switching from normal. running of this kind to lateral running,firstly, a lever-type lateral running mode switch (not shown) isoperated, and by inclining a lever, the turning cylinder 53 is caused toextend. Thereby, the link member 52 is moved in the direction of theextension, and in accordance with this movement, the turning members 24are rotated about the vertical axis 27.

Since the link member 52 is positioned in a crossing manner with respectto the right and left front wheels 3, as illustrated by the virtuallines in FIGS. 9 and 10 and the diagrams in FIG. 11(b) and FIG. 13, thetwo turning members 24 rotate in mutually opposite directions about thevertical axis 27, whereupon the two front wheels 3 are steered to a 90°position (in a perfectly lateral direction) with respect to the vehiclebody 2.

After steering the front wheels 3 in this fashion, by supplyinghydraulic pressure from the pair of pumps 31 driven by the engine 30 tothe corresponding hydraulic motors 21 by means of the pipes 32, thefront wheels 3 are driven forwards and rearwards, and hence the forklift 1 is enabled to travel laterally in the right and left direction.In so doing, the hydraulic motors 21 corresponding to the right andleft-hand front wheels 3 are controlled in such a manner that theyrotate in opposite directions. The right and left-hand pair of rearwheels 54 forming a turning caster system perform follow-up steering.

When performing lateral running in this manner, in other words, in alateral running mode where the front wheels 3 are steered to a 90°position with respect to the vehicle body 2 (in a perfectly lateraldirection), the turning cylinder 53 is slightly retracted to steer thefront wheels 3 inwards by a small angle (in a range of about 5°) asillustrated in FIG. 14(a), or the turning cylinder 53 is slightlyextended to steer the front wheels 3 outwards by a small angle (in arange of about 50) as illustrated in FIG. 14(b), whereby deviation froma straight course caused by road surface conditions or due to weightbalance can be readily corrected.

By steering (moving) the front wheels 3 inwards or outwards by a smallangle (in a range of about 5°), it also becomes possible to change thedirection of the fork lift 1 to some extent during lateral running.Further, if it is structurally permitted, by taking the steering angleof the front wheels 3 to be greater than 5°, it also becomes possible toperform turning during lateral running.

In the third embodiment described above, the rear wheel 54 was describedas a parallel pair of right and left-hand wheels, but it is alsopossible to adopt a pair of right and left-hand rear wheels 54 disposedsimilarly to the front wheels 3. In this case, one of the pair of rightand left-hand rear wheels 54 may be of a steering-type controlled by ahandle wheel and the other may be of a turning caster-type, and whenswitching to lateral running, the former one of the rear wheels 54 isforcibly steered by means of a cylinder or the like.

Next, a fourth embodiment of the present invention will be describedwith reference to FIG. 15 to FIG. 20.

In this fourth embodiment, constituent elements which are the same orsubstantially the same as those in the first embodiment described above(FIG. 1-FIG. 4) are similarly labelled, and detailed explanation thereofis omitted here.

The mounts of hydraulic motors 21 are attached in a lateral direction tovertical plate sections of T-shaped turning members 60, and the lateralplate sections of the turning members 60 are installed rotatably about avertical axis 63 with respect to the vehicle body 2 via a bearing 61 andvertical axle 62. Here, a vertical axis 63 is positioned away from afront wheel ground contact axis 64 located at the central portion of thefront wheel 3, with a space equal to a lateral-directional displacementL therebetween.

Rotating means 70 for rotating the turning members 60 is provided, andthis rotating means 70 is constituted in such a manner that the twoturning members 60 are turned in the same direction by means of a commonactuation device. In other words, the rotating means 70 comprises aturning cylinder (one example of a common actuation device) 71, and amain body 71 a of this turning cylinder 71 is installed swingably on thevehicle body 2 via a vertical pin 72. A piston rod 71 b is coupled in arelatively rotatable fashion to a link 73 fixed to one of the turningmembers 60 via a vertical coupling pin 74.

Two arms 75 projecting from the right and left-hand vertical axles 62are mutually coupled in a relatively rotatable fashion by means of alink member 76 and coupling pins 77. The two coupling pins 77 aredisposed in the same front-and-rear direction with respect to thevertical axes 63, and consequently, when the right and left-hand frontwheels 3 are steered in the front-and-rear direction, the link member 76is positioned parallel to the front wheel axis between the two frontwheels 3.

Therefore, by actuating the turning cylinder 71 to rotate one of theturning members 60 via the link 73, one of the front wheels 3 on oneside is steered about the vertical axis 63 and caused to face directlysideways, and the other front wheel 3 is steered about the vertical axis63 and caused to face directly sideways by means of the arm 75, linkmember 76 and the like. In other words, with the rotating means 70, byactuating the common turning cylinder 71, the right and left-hand frontwheels 3 are rotated (steered) mutually in the same direction to faceperfectly sideways respectively. The elements 71 to 77 and the likeconstitute one example of the rotating means 70.

The operation of the fourth embodiment described above will be explainedbelow.

The solid lines in FIG. 15 and FIG. 16, and the diagrams in FIG. 17,FIG. 18 and FIG. 20(a) illustrate linear movement during normal running,in which the pair of right and left-hand front wheels 3 and the pair ofright and left-hand rear wheels 4 are facing in a front-and-reardirection. Here, the rotating means 70 operates such that the turningcylinder 71 is extended, the link 73 is moved in this direction ofextension, and the link member 76 is placed in parallel to the frontwheel axis, so that the right and left-hand front wheels 3 are orientedin the front-and-rear direction.

As described above, a two-pump two-motor type hydraulic drive system isadopted as a driving system for the fork lift 1, so that turning duringlinear movement in a normal running mode can be effected by controllingthe steering direction of the two front wheels 3 and the difference inrevolutions thereof by means of the handle wheel. In other words, asillustrated by virtual lines in FIG. 18(a), for example, when speed ofrevolutions on the right-hand side, F, is raised higher than the speedof revolutions on the left-hand side, f, the fork lift 1 will perform aleft-hand turn due to the resulting difference in revolutions. In thiscase, the right and left pair of rear wheels 4 will perform a follow-upturning while automatically changing the orientation thereof to thedirection of the steering. A right-hand turn can be performed in asimilar manner by increasing the speed of revolutions on the left-handside to be higher than that on the right-hand side.

When switching from normal running of this kind to lateral running, alever-type lateral running mode switch (not shown), for example, isoperated first, and then the rotating means 70 is actuated. Morespecifically, in the rotating means 70, the turning cylinder 71 iscaused to retract by inclining the lever. Thereby, one of the turningmembers 60 is rotated about the vertical axis 63 via the link 73 and thelike, whilst the other turning member 60 is rotated about the verticalaxis 63 by means of the vertical axle 62, arm 75, link member 76 and thelike.

Since the link member 76 is positioned in parallel to the front wheelaxis, the two turning members 60, as illustrated by the virtual lines inFIG. 15 and FIG. 16, and the diagrams in FIG. 17, FIG. 18 and FIG.20(b), are rotated in the same direction about their vertical axes 63,and the two front wheels 3 are steered to a 90° position (in a perfectlylateral direction) with respect to the vehicle body 2. Moreover, sincethe vertical axes 63 are distanced from the respective front wheelground contact axes 64 by a space equal to the lateral-directionaldisplacement L, the two front wheels 3 which have been steered to a 90°position (in a perfectly lateral direction) to be directed laterally aredistanced from each other in the front-and-rear direction by adisplacement in lateral movement, 2L, that is double the displacement L.

By steering the front wheels 3 to a 90° position in this way, thelateral running mode can be assumed. Consequently, by supplying thehydraulic pressure from the pair of hydraulic pumps 31 to thecorresponding hydraulic motors 21, the front wheels 3 are driven inforward and reverse directions, and the fork lift 1 can perform lateralrunning in the right-and-left direction, as illustrated in FIG. 18 andFIG. 20(b). Here, during lateral running in a linear direction, thehydraulic motors 21 corresponding to the right and left-hand frontwheels 3 are controlled in such a manner that the respective directionsof rotation and revolutions are the same.

When lateral running is performed in this way, in other words, when thelateral running mode in which the two rear wheels 4 are steered 90° (ina perfectly lateral direction) with respect to the vehicle body 2 istaken as a neutral state, and a steered angle of the handle 16 or rearwheels 4 from this state is detected by a sensor or the like, and bychanging the input and output to and from the hydraulic controller,different speeds of revolutions are given to the right and left-handfront wheels 3 respectively, thereby to effect turning.

In other words, in lateral running to the right-hand side as illustratedin FIG. 19(a), if the right-hand side front wheel 3 is set to a highspeed of revolutions F and the left-hand side front wheel 3 is set to alow speed of revolutions f, a right-hand turning force acts on thevehicle body 2 due to the difference in speed of revolutions between thefront wheels 3 which are distanced by the lateral running displacementof 2L, and lateral running to the right is performed while turningtowards the rear side. Moreover, in lateral running to the right-handside as illustrated in FIG. 19(b), if the left-hand side front wheel 3is set to a high speed of revolutions F and the right-hand side frontwheel 3 is set to a low speed of revolutions f, a left-hand turningforce acts on the vehicle body 2 due to the difference in revolutionsbetween the two front wheels 3 distanced by the lateral runningdisplacement 2L, and lateral running to the right-hand side is performedwhile steering towards the front side.

In lateral running of this kind, since a lateral running displacement 2Larises between the two front wheels 3, a turning force to the left orright can be applied to the vehicle body 2, simply by applying differentspeeds of revolution to the right and left wheels of the front wheels 3by way of operating the handle or the like, and hence lateral runningcan be performed whilst turning the vehicle in the longitudinaldirection (front-and-rear direction) thereof. Further, it is possible toreadily correct deviation from the straight course caused by the roadsurface conditions or the weight balance. Similar control can be alsoachieved during lateral running to the left-hand side.

In the fourth embodiment described above, a system was illustrated inwhich the turning cylinder 71 is used as an actuation device of therotating means 70, this may also comprise a system where the steering toa 90° position is performed by means of a motor or the like. Moreover,the rotating means 70 was described as such that the turning cylinder 71is used as a common actuation device for the right and left-hand wheels,but it is also possible to provide separate actuation devices on theright and left-hand sides.

Next, a fifth embodiment of the present invention is described withreference to FIG. 21 and FIG. 22.

In this fifth embodiment, constituent elements which are the same orsubstantially the same as those in the first embodiment described above(FIG. 1-FIG. 4) are similarly labelled, and detailed explanation thereofis omitted here.

The pair of right and left-hand front wheels 3 and the pair of right andleft-hand rear wheels 4 are provided respectively to be steerable 90°(laterally steerable) with respect to the vehicle body 2. The frontwheels 3 are drive wheels, and each comprises an actuation device forperforming a 90° steering. The mast 6 disposed at the front end of thevehicle body 2 is disposed such that the lower portions thereof arepositioned between the right and left-hand front wheels 3 when in anupright attitude. The mast 6 is attached rotatably in the front-and-reardirection with respect to the vehicle body 2 by means of a coupling axle80 which is positioned in the lateral direction of the vehicle and abovethe front wheels 3.

A tilt cylinder 81, which is an example of a rotational drive device forperforming front-and-rear rotation of the mast 6, is provided betweenthe mast 6 and the vehicle body 2. When the mast 6 is rotated by thetilt cylinder 81, the lower portions of the mast 6 swings out forwardsand moves to a position where the mast does not interfere with thesteering of the front wheels 3.

The operation of the fifth embodiment of the present invention describedabove will be explained below.

The solid lines in FIG. 21 show a normal running mode. Here, the tiltcylinder 81 is retracted so that the mast 6 is in a standing positionand the lower portion thereof is positioned between the right andleft-hand front wheels 3. Therefore, the fork lift 1 can be formedwithout creating a long front overhang. By operating the tilt lever andactuating the tile cylinder 81, the mast 6 can be rotated (tilted) aboutthe coupling axle 80, and hence the attitude of the forks 13 in the forklift 1 can be changed via the lift brackets 12 and the like.

When switching from normal running of this kind to lateral running, alateral running mode switch (not shown) is operated first, and the tiltcylinder 81 is extended greatly. By extending the tilt cylinder 81, themast 6 is rotated (tilted) about the coupling axle 80, and asillustrated by the dotted lines in FIG. 21, the lower section of themast 6 swings out forwards from between the front wheels 3, and moves toa position where the mast does not interfere with the steering of thefront wheels 3.

Next, the turning lever (not shown) is operated, and the front wheels 3are steered to a 90° position (steered perfectly laterally) with respectto the vehicle body 2, by a 90°-steering-operation device, asillustrated by the virtual lines in FIG. 1. In this, the 90° steering ofthe front wheels 3 is performed smoothly without any hindrance becausethe lower section of the mast 6 has been moved to the position where themast does not interfere with the steering.

After performing the steering of this kind, the tilt cylinder 81 isactuated to retract itself by the feedback from the sensor. Thereby, themast 6 is rotated about the coupling axle 80 to assume a standingposition, as illustrated in FIG. 22, and the lower section of the mast 6is made to oppose the side faces of the front wheels 3 from the forwarddirection, so that the fork lift 1 can perform lateral running, withoutthe front overhand becoming long.

In the fifth embodiment described above, the tilt cylinder 81 wasdescribed as a rotation drive device, but this may be a screw drive, alinkage system or the like.

In the respective embodiments described above, the turning caster systemwhich performs follow-up steering was adopted as the pair of right andleft-hand rear wheels 4, or for the parallel pair of right and left-handrear wheels 54, but similarly to the front wheels 3, such system as toeffect turning forcibly by means of a cylinder or the like may beadopted. Moreover, it is also possible to adopt a steering-type wheeloperated by the handle wheel as one of the rear wheels 4, and a turningcaster-type wheel as the other rear wheel 4. In this case, whenswitching to lateral running, the former rear wheel 4 is forciblysteered by a cylinder or the like.

What is claimed is:
 1. A fork lift with a laterally traveling systemincluding a pair of right and left-hand front wheels and a pair of rightand left-hand rear wheels each provided on a vehicle body, characterizedin that: the front wheels and the rear wheels are respectively providedto be steerable; the pair of right and left-hand front wheels arerespectively coupled in linkage to driving shafts of travel drivedevices; each of said travel drive devices is attached to turningmembers provided to be rotatable about a vertical axis with respect tothe vehicle body, and rotating means is provided for rotating theturning members; said rotating means comprising coupling sections of theturning members disposed in mutually opposing directions in afront-and-rear direction with respect to the vertical axis, a linkmember in a lateral direction of the vehicle, the link member beingcoupled between these coupling sections to enable the turning members tobe relatively rotatable, and an actuation device for moving this linkmember in the lateral direction of the vehicle; and a mast is providedon the front end of the vehicle body, and forks are provided on themast.